I do agree to take chubby out since the rest of the premise doesn't seem to relate to her weight. Since you have more room here to expand, I agree to add in a little more of the resistance. Why does she want/need to get over the ex by the end of summer? What threat or challenge does Ren pose to Ivy's dreams? If her goal is say to avoid all guys and relationships, and he thwarts that, for example. What choice does she need to make is another good way to get the stakes of the story in there.

Yeah, unless he dumps her BECAUSE she's chubby and this story is about either weight-loss or coming to terms with one's own physical image, I think you need to remove chubby.

Aside from that, it isn't clear why she has to get over the jerk in one summer. What happens at the end of the summer? And why would she not want to fall for this newcomer? As written, it sounds like exactly the thing she SHOULD do!

I think you need to explain what happens at the end of the summer. Is she going off to college? Will she have to face this jerk who dumped her when she gets there? Right now the ticking clock of one summer feels arbitrary.

I agree with the suggestions you've already received. WHy does she 'have' to get over him? WHat happens if she doesn't? And why must she do it before summer's end? ANd why doesn't she want to fall from Ren.

And you don't need chubby unless being chubby is somehow relevant to all this.

WHat is your MC really trying to achieve? Coming to terms with her weight. Liking herself as she is? Whatever it is, make that evident in the logline.